1. Field of the Invention
The present invention relates to improved compositions comprising polyvinyl chloride resin and, more especially, relates to improved paste compositions comprised of said polyvinyl chloride [PVC] resin and which paste compositions are characterized by enhanced fluidity, longer pot lives, enhanced adhesive properties, and markedly improved workability attributes.
2. Description of the Prior Art
Various paste compositions comprising a polyvinyl chloride resin are well known in the art and are widely used on an industrial basis for the coating of certain substrates, such as textiles, paper, and steel, and which also have been utilized for the preparation of certain films and a variety of other molded articles, for example, by rotational casting, spread-coating, spraying, dipping, slushing, and the like. Representative products thus produced consistent with the immediately aforesaid comprise the vinyl leathers, polyvinyl chloride resin coated steel plates, waterproof canvases, coated textiles and cloths, industrial gloves, printing rolls, shoe soles, various foamed articles, dolls, cushions, and the like.
Typically, however, the workability of the known PVC paste compositions is controlled merely by adjusting the various viscosities thereof. It is therefore of course required that the given polyvinyl chloride paste composition exhibit the proper fluidity for the particular paste treatment or application contemplated [which proper fluidity usually iss synonomous with lower viscosity] and it is also required that any change in said fluidity upon passage of a given period of time be slight [or, in other words, the paste must have a relatively long pot life].
Furthermore, the degree of adhesion or adhesiveness of the PVC resin to a given base substrate is also quite important, since in many instances such paste compositions are used for the purpose of applying polyvinyl chloride resin to the surfaces of various textiles and cloths, papers, metals and/or plastics. And it should additionally be borne in mind that various high frequency welding techniques, e.g., ultrasonic bonding, have been used to adhere laminae comprised of the vinyl chloride resins. From this point of view, the degree of adhesiveness of a polyvinyl chloride layer to its intended substrate material, as well as the degree of cohesiveness of the polyvinyl chloride resin itself, too are quite significant.
It is also well known in the art that the fluidity of a given polyvinyl chloride paste composition can be improved [or its viscosity decreased] by adding to the composition substantial amounts of an inert diluent such as trichloroethylene ["trichlene"]. However, such a method for improving the fluidity characteristics of the selected PVC paste composition suffers from the fatal defect, because of the highly volatile nature of the diluent, of giving rise to the evolution of highly noxious vapors and, hence, is highly unsanitary and ambient polluting. Moreover, the aforementioned change in fluidity of such a paste or the increase in the viscosity thereof over a given period of time is objectionally large.
It has also been proposed to improve the fluidity of the polyvinyl chloride paste compositions by adding thereto certain surface activators comprising certain derivatives of the polyhydric alcohols. Compare U.S. Pat. No. 2,657,186 to Klein et al. However, such additives are to a large extent incompatible with polyvinyl chloride and, accordingly, characteristically bleed out of paste compositions of this type. Moreover, such additives concomitantly effect a decrease in the adhesive properties of the polyvinyl chloride paste.
It is similarly known in the art that upon the formulation of a given paste, same should not become swollen or expanded by any plasticizer or solvent content thereof during or upon storage. Contrariwise, at the point in time of the intended use of such paste compositions, it is of course preferred that same be readily, uniformly swollen or expanded to form a more workable gel phase. But, since the aforesaid requirements can be said to be inconsistent or even mutually exclusive, the art is accordingly replete with various efforts compromising the noted requirements and seeking to arrive at any happy medium. Unfortunately, however, such truly satisfactory alternative has yet to be determined. And, thus, under the circumstances above outlined, the various paste compositions, per se, the conditions for the preparation or formulation thereof, the conditions under which the same are aged, and the conditions for the utilization or working thereof, are presently merely selected experimentally, depending upon the ultimate goal to be achieved.
Also, the fluidity of a typical paste composition and more particularly, any change therein over a given period of time are much more complex variables for all practical intents and purposes than above indicated, since various fillers such as calcium carbonate, baryte, and calcined clay, and various coloring agents, such as pigments, are typically incorporated into the composition, in addition to the usual resin, plasticizer, low boiling point solvent, and gelling agent. Hence, pot life upon the formulation of such a paste is indeed quite short.
Consequently, a serious need exists in the art for an improved polyvinyl chloride resin paste composition exhibiting enhanced characteristics of fluidity and adhesiveness, which is more easily worked, which does not exhibit a marked change in fluidity upon passage of a given period of time and which will not give rise to pollution of the atmosphere.